In general, metals are joined together by brazing technique using brazing filler metals. Kinds of the brazing filler metals used such as copper-phosphorus and nickel brazings are various depending on kinds of metals to be joined together.
Copper-phosphorus brazings are brazing filler metals exclusively for copper and copper alloys and are generally constituted by copper added with 4-9% of phosphor in mass percentage so as to lower melting points. Among the brazing filler metals, copper-phosphorus brazing called BCuP-2 in JIS standard Z3264 is an copper alloy add with 6.8-7.5% of phosphor and is widely used for brazing in a gas appliance, a refrigerating machine and other copper products.
The copper-phosphorus brazing called BCuP-2 in the JIS standard, which has inferior workability and is hardly rolled into sheet due to lack of ductility at room temperature, is generally on the market in the form of wire, rod or powder.
For example, fins of a plate-type heat exchanger in the form of pressed metal sheets into corrugation are provided by brazing ridges and valleys of the sheets together. This require a process of setting wire- or powder-like copper-phosphorus brazing over portions to be joined of the metal sheets, which is troublesome and tends to block improvement in productivity.
Thus, it is expected that if a clad material comprising a metal sheet as base material and a brazing filler metal layer formed on the metal sheet were produced and used as fin blanks to be brazed for the above-mentioned plate type heat exchanger, the setting process of the brazing filler metal might be omitted to allow carrying out all production processes in succession and in an automated manner, resulting in improved productivity and reduced costs.
FIG. 1 is a schematic view showing a producing apparatus used for carrying out a method for producing a clad material through usual rolling. The producing apparatus comprises a base material uncoiler 3 for uncoiling a base material coil 2 which is a coiled base material 1 in the form of metal sheet, a foreign material uncoiler 6 for uncoiling a foreign material coil 5 which is a coiled foreign material 4 in the form of different kind of metal sheet, a cladding rolling mill 7 for rolling the base and foreign materials 1 and 4 in an overlapped manner and a clad material coiler 10 for coiling the clad material 8′ rolled in the rolling mill 7 as clad material coil 9.
In the method for producing the clad material shown in FIG. 1, the base and foreign materials 1 and 4 are uncoiled from the coils 2 and 5 by the uncoilers 3 and 6, respectively. The uncoiled base and foreign materials 1 and 4 are overlapped together and rolled by the rolling mill 7 into the clad material 8′ which is coiled by the coiler 10 into the clad material coil 9.
The clad material 8′ from the rolling mill 7 has a cross-section as shown in FIG. 2 such that the foreign material 4 is press-fixed to the base material 1 to provide a brazing filler metal layer 11′.
As the base material 1, various kinds of metals may be used. It has been proposed, for example, to produce a clad material 8′ constituted by a copper sheet as base material 1 and a sheet of copper-phosphorus alloy as foreign material 4, said copper-phosphorus alloy sheet having below-standard phosphor content (3% or so) in mass percentage less than 4.5% in the standard copper-phosphorus brazing filler metal called BCuP-1 so as not to be broken upon rolling.
State of art concerning the above-mentioned clad material has been disclosed, for example, in Patent Literature 1.    [Patent Literature 1] JP 2004-114158A